After I have removed vertices, error says "loop in parent"
I did not look at .blend file, but I will explain Loop in parents. It means, so you are trying to make infinite loop of parents(which would cause .blend to crash imediately, so Blender has blocked it). So, if you have set your character as Parent of your Bones, you can't set bones as paernt to your character, otherwise, the parentation principal will be infinite loop. YOu can try selecting Bones and doing ALT + P and than Click with LMB on Clear Parent. Than do the same with char(optional). After that parent char to Bones. Hope this helps.